Born or living first, or before the others, as a son, daughter, brother, etc.; first in origin. See Elder.

the offspring who came first in the order of birth

first in order of birth; "the firstborn child"

Eldest is the second book in the Inheritance trilogy, written by Christopher Paolini. It is the sequel to Eragon. Eldest was first published in hardcover on August 23, 2005, and was released in paperback on September 2006.